## Algebra: A Combined Approach (4th Edition)

$\dfrac{4a}{a^{2}+2a-15}-\dfrac{12}{a^{2}+2a-15}=\dfrac{4}{a+5}$
$\dfrac{4a}{a^{2}+2a-15}-\dfrac{12}{a^{2}+2a-15}$ Evaluate the substraction of the two rational expressions: $\dfrac{4a}{a^{2}+2a-15}-\dfrac{12}{a^{2}+2a-15}=\dfrac{4a-12}{a^{2}+2a-15}=...$ Factor the denominator and take out common factor $4$ from the numerator. Then, simplify: $...=\dfrac{4(a-3)}{(a+5)(a-3)}=\dfrac{4}{a+5}$